Add spaghetti sauce to the drained ground beef. Using a 9x13 baking pan, spread enough spaghetti sauce on the the bottom of the pan to coat it so the lasagna noodles won't stick. Lay 3 cooked lasagna noodles side by side lengthwise on top of the sauce. Spread the noodles with a generous amount of the ground beef-spaghetti sauce mixture. Top this layer with some of the thinly sliced pepperoni. Sprinkle with 1 cup of the shredded mozzarella cheese. Top with 3 more lasagna noodles and repeat spreading with ground beef-spaghetti sauce mixture, top with sliced pepperoni, and sprinkle with 1 cup of shredded mozarella cheese. Top with the remaining 3 cooked lasagna noodles. Spread with spaghetti sauce mixture, top with the last cup of shredded mozarella cheese and sprinkle generously with grated Parmesan cheese. Cover with aluminum foil and bake in a 350 degree oven for 20-30 minutes. I begin checking after 20 minutes and remove from the oven when the cheese on the top is melted and bubbly.

Helpful Tips:

I've used many different brands of spaghetti sauce, but my family prefers Ragu Traditional. It seems to have just the right amount of seasoning in it.